In the manufacture of semiconductor multi-chip hybrids and systems, the yield of the hybrid is a function of the yield of the interconnecting substrate, and the passive and active circuit components. The interconnect and passive components in the hybrid can be visually and electrically inspected prior to assembly, and their properties remain fairly constant over the expected lifetime of the hybrid. However, the failure rate of an integrated circuit has been shown to vary with time. Early in the life of an integrated circuit, a relatively large number of devices will fail, due to defects introduced in the manufacturing process. Only by exercising the die during a "burn-in" test, will the initial failure rate drop to an acceptable level.
There are no techniques currently available which allow burn-in testing of integrated circuits without damaging the die. If the die are not burned-in, then the yield loss for each device can drastically reduce the yield of the hybrid. Re-work of Tape Automated Bonding (TAB) and flip-chip mounted devices, which are used in hybrid circuits, is very labor intensive and time consuming. The re-work process is difficult to automate in a production environment, and re-worked hybrids often exhibit lower reliability than parts which do not require repair. The high costs associated with re-work indicates the importance of incorporating devices which exhibit low failure rate in the hybrid. If potentially defective die can be detected before they are committed to a package, then the subsequent yield for the completed hybrid will improve.
There are currently two techniques for the burn-in testing of integrated circuits. The most widely used method involves placing the device in a package and wire-bonding the extra or enlarged test pads to signal leads in the package. The packaged device is then plugged into the burn-in test system for testing. After testing, the wire bonds are broken off before the die is inserted on the hybrid. The other test method is to use a conventional probe card for burn-in testing. This probe card is similar to the card which is used for functional testing of the device. The problem with these test methods is that they tend to damage the integrated circuit die.
Removal of the bond wires tends to damage the bond pads on the device, resulting in lower yielding bonds. Burn-in testing using a probe card also damages the test pads on the device. The thermal expansion of the probe needles and the scrub-in of the probe tips may tear the test pads and crack the protective oxide on the device. Hybrid manufacturers must currently decide between assembling hybrids with pre-tested, but damaged devices, or chips which have not been tested.